Treasury of Scripture Knowledge
You should know, then, that people who have faith are [truly] God's children.
Now, brothers, you [Christians] are children of the promise [made to Abraham. See 3:29] just like Isaac, [Abraham's son] was.
He received the sign of circumcision as a seal [confirming] that he had been [considered] righteous because of the faith he had before being circumcised. Thus, he became the [spiritual] father of all people who believe [in God], even though they have not been circumcised, so that they could be considered righteous [by their faith].